Attention has been directed, in the past to the patching of materials which are secured in place such as is the case with upholstered furniture and billiard table cloth. The incentive for such attention, of course, arises not only because of the high cost of replacement of the material involved, but also because of frequent inability to obtain identical replacement material and because of the high cost of labor.
There is a variety of prior art techniques for repairing such materials in situ. Most require an adhesive backing material for forming a void into which cementitious material including fibers to match the repaired material is disposed. In some techniques, laminate patches are preformed to be cemented into place. Such techniques are perhaps adequate for fabrics which are secured in place as, for example, billiard table cloths, where little movement of the repaired material is possible. Experience, on the other hand, indicates that such techniques are not well suited for materials which are intended for movement under pressure as is the case with upholstered furniture.
The failure of prior art techniques is particularly apparent with plastic materials such as leatherettes and, of course, leather which the plastics so closely imitate. These make repairs obvious, but are intended to stretch in use thus taxing the structural capabilities of any patch with less flexible properties.
In my U.S. Pat. No. 3,713,926 issued Jan. 30, 1973, I disclose a plastic repair procedure in which a plastic film forming material, in paste form, is applied to a damaged area in a plastic material and covered with graining paper. The graining paper functions, with the surrounding undamaged portion of the plastic and with an adhesive backing material, to form the damaged area into a mold in which the paste is cured in situ in the presence of heat. The heat is supplied by a flat hot surface applied to the graining paper. The surface functions to compress the mold as it cures the patch.
A problem arises when the flat hot surface is pressed against the patch. If the flat hot surface is defined by the face of a familiar household iron, the iron is, typically, sufficiently large to extend beyond the typical piece of graining paper and the iron frequently removes the graining from the formerly undamaged material surrounding the patch and beyond the graining paper. This undesirable result can occur, at sufficiently high temperatures frequently realized with an iron, even through the graining paper. Further, different types of plastics react differently to heat. Some may melt irreversibly when exposed to the flat hot surface even at relatively low temperatures. This too can occur through the graining paper though perhaps at a higher temperature.
One solution to this problem is to employ a small special iron to avoid heating large areas of the undamaged material and, in addition, to move the iron with respect to the vinyl release (graining) paper. Indeed, repair kits, presently being sold, include soldering irons with disc-like tips which provide heat over a circular area of about an inch, well within the confines of the typical graining paper. With a little practice, very successful patches are achieved by movement of an instrument of this type with respect to the graining paper. But such an instrument is expensive, particularly if it includes a thermostat to regulate the temperature of the tips to an acceptable 300.degree.- 350.degree.F. Unregulated household irons, on the other hand, when plugged in, increase in temperature relatively quickly to a sufficiently high temperature to cause discoloration of the undamaged plastic. Of course, the graining paper, commonly called "vinyl-release" paper, is opaque and does not allow visual inspection of the curing process. Accordingly, it is difficult to guard against discoloration. Frequently, a perfect patch is formed in the middle of an area of discoloration.
The special iron sometimes avoids the discoloration problem for the most part particularly as long as the iron is moved quickly with respect to the graining paper and the heat from iron is perfectly regulated.
In my copending application Ser. No. 386,345, filed Aug. 7, 1973 now Pat. No. 3,887,413, the undamaged material surrounding a damage to be repaired by a heat responsive, plastic repair procedure is preconditioned to avoid damage, resulting from contact with the requisite hot flat surface which cures the patch, whether or not a special iron is used. Preconditioning is achieved by applying a paste comprising a mixture of Bentonite and talc (both clay derivatives) in water onto the undamaged material around the damage prior to filling the damaged area with the repair forming paste. The preconditioning paste insulates the plastic from the heat of the iron and allows a patch to be cured in situ without discoloration or loss of graining even if the flat, hot surface remains unmoved against the protected undamaged plastic during the patch curing process.
Although the paste avoids the previously described problems of discoloration and the necessity of a special iron, the paste is difficult to remove and has a tendency to attack the graining paper thus limiting the use of that paper to a single repair. Moreover, unless care is taken the insulating paste may be moved into the damaged area by the movement of the iron. If this occurs, the patched area can be ruined since the paste prevents proper curing if it is moved into the damaged area during the curing process.